This invention relates in general to dynamoelectric or electromagnetic machines and, more particularly, to electromagnetic actuators.
Electromagnetic actuators have a wide variety of applications ranging from the movement of aircarft control surfaces to the movement of active suspensions in passenger vehicles, as well as many other applications. In general these motor-actuator devices include a moving element or ram which moves with respect to a fixed element referred to as a stator. Electromagnetic actuators are often employed to eliminate hydraulics and gears, thus achieving reductions in both weight and volume in a particular application. Other desirable features of electromagnetic actuators are relatively high efficiency, wide bandwidth and "power by wire", or ability to operate on electrically-supplied power.
Linear induction machines have been known for a number of years and have been used to deliver force in automation and transportation applications. Although linear induction machines represent an important development, known types of machines unfortunately are generally undesirable when used as electromagnetic actuators due to their low efficiency and power factor as well as high moving element losses. Other machines, such as wound field linear synchronous inductor machines, have been employed in transportation applications and some low power actuator applications. However, linear synchronous inductor machines suffer from low force densities due to the inductor principles required for brushless operation.
Linear reluctance machines also have been known for some time and have found application as low power actuators. Unfortunately, linear reluctance actuators have relatively low efficiency and low force density. Also, linear reluctance actuators tend to suffer from force pulsations and undesirable noise. In certain applications, such as in automobile suspensions for example, such pulsations and noise can be critical factors.
Permanent magnet linear actuators are commonly used in computer disk drives for moving the head which reads the disk media. Such permanent magnet linear actuators, however, have a relatively short stroke and thus are unsuitable for applications which require a relatively long stroke such as in active automotive suspensions.